I built a 8 ft halfpipe like xtremeskaters 2 years ago and im replacing the masonite and would like to waterproof it. ive heard about spar urethane and was wondering how much spar i will need and how to apply it

i did the spar urethane im in florida and its held up through some heavy rain just coat the backs and sides really good before you put it on then i recomend putting a ton of screws in then do atleast 2 coats im not sure what snow will do to it though